Epoxy resin emulsions have been known for a long time and have been diversely described in the literature. The term “epoxy resin emulsions” is understood below to refer to aqueous systems which comprise emulsified or dispersed epoxy resins.
Epoxy resin emulsions are used predominantly as coating materials in combination with suitable curing agents. Fundamental differences of epoxy resin emulsions versus other types of emulsions are firstly the nature of the stabilization, and secondly the average molar mass of the epoxy resins used.
Hence, there are numerous patent applications on the preparation of solid-resin dispersions wherein the average molecular weight of the epoxy resin is in the range between 900 and 1200, and which have an epoxide equivalent weight (EEW, Epoxy Equivalent Weight), in the range of about 450-600. Most of the emulsifiers used in this case possess epoxide groups and therefore become part of the cured coating; a term also used in this context is that of reactive emulsifiers. In the course of the solid-resin synthesis, reactive emulsifiers are incorporated into the polymer that forms.
Epoxy resin emulsions generally contain certain amounts (typically 3-13%) of solvents for the purpose of improving film formation in the subsequent application, or of reducing the in-process viscosity during preparation of the dispersion, and also comprise reactive diluents and further additives for improving the storage stability.
In the preparation of liquid-resin emulsions it is usual to use external emulsifiers for the purpose of stabilization. These are usually specialty surfactants which in the subsequent application do not become part of the coating and are therefore able to diffuse out of the cured film.